I was able to buy injectors, nozzle holders with o rings, and seals for under $200 from autohaus for my 450sl.
They were great to deal with and shipped quick. Don't make the mistake I did and order the o-rings seperately as the come with the nozzle holders.
Yes-- get both the seals and the holders, and don't scrimp on aftermarket versions-- it's just not worth it. I'd also throw in all the upper rubber parts (list below)-- again, get the real deal. The trucktec parts at Autohaus AZ are not worth the effort. Parts.com has the stuff. The injectors and seals from Autohaus are OK, in my experience.
Oh, and to get the injectors out, you disconnect the fuel lines and also need to take out the keeper clips, which I recall have a 5mm allen bolt. Pretty self-explanatory when you're in there.
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